Lubricating oil compositions containing ester of mercapto acid and a phosphonate



United States Patent 1 3,206,401 LUBRICATIN G OIL COMPOSITIONS CONTAIN-ING ESTER 0F IVERCAPTO AClD AND A PHOSPHONATE Rosemary OHalloran, Union,NJ, assignor to Ease Research and Engineering Company, a corporation ofDelaware No Drawing. Filed Jan. 3, 1%1, Ser. No. 80,016 Claims. (Cl.25246.6)

This invention relates to lubricating oil compositions which are usefulin automobiles as automatic transmission fluids, as rear axlelubricants, and which are particularly useful in transaxle systems.Specifically, the invention is directed towards a mineral lubricatingoil containing an alcohol ester of a mercapto acid in combination with aphosphonate, which composition may contain other additives.

Recently, in certain makes of automobiles the transmission and the rearaxle systems have been combined into a single mechanical unit locatedproximate the rear wheels of the automobile. This combined unit is knownas a transaxle unit and is primarily designed to eliminate theconventional hump extending along the floor of the automobile. Thecombined mechanism requires a lubricant which has the properties of bothan automatic transmission fluid and a rear axle lubricant. Thelubricant, therefore, must be extremely stable to heat and oxidation,have good antiwear properties and at the same time have the extremepressure properties required for the hypoid gears associated with therear axle. In addition to these basic properties, a transaxle lubricantmust be inert to a wide variety of materials used in the construction ofthe combined units. The problem of formulating such a lubricant has beenparticularly difiicult since the conventional extreme pressure additivespreviously used in rear axle lubricants tend to attack the rubber seals,the nylon gears, and the resin bonded paper clutch discs of thetransmission system. On the other hand, many of the mild extremepressure additives used in transmission oils were insutficient in theirextreme pressure properties to impart the desired degree of extremepressure properties suitable for the rear axle unit. The presentinvention is based upon the discovery that a certain narrow class ofalcohol esters of mercapto acid in combination with certain phosphonatessolved the problems encountered. Both these types of compounds werefound to be stable and had no bad effect upon the materials encountered.The ester additives primarily contribute the necessary extreme pressureproperties, While the phosphonates contribute valuable antiwearproperties.

The mercapto acid esters operable in the invention are those having thegeneral formula:

HS(CH ),,COOR

wherein n is an integer of l to 4 and R represents an alkyl radical of aC to C alcohol, e.g. a C to C 3,26,4fll Patented Sept. 14, 1965straight-forward esterification techniques, with or without catalyst,and preferably using a solvent such as hexane as a Water-entrainingagent. If desired, the solvent-ester mixture may be washed with waterand neutralized with sodium bicarbonate solution (if an acid catalystsuch as NaHSO -H O is used), followed by more water washing beforestripping and filtering.

In addition to being prepared by straight-forward esterificationreactions between the alcohol and acid, the ester can also be preparedby ester interchange and other methods. For example, the ester ofchloroacetic acid can be first made and then converted to the esterdisulfide of mercaptoacetic acid by reaction with Na S or by reactionwith thiourea followed by reaction with NaOH.

While the above type of mercato acid ester has been found particularlyeffective, other similar sulfur-containing esters had been foundineffective. Thus, in order to obtain the desired extreme pressureproperties, it appears desirable that the sulfur atom of the compound belocated proximate the end of the molecule. For example, esters preparedfrom materials having the sulfur in the center portion of the molecule,such as Kromfax glycols (plus fatty acids) having the formula:

while having excellent oxidation stability and good rubber resistance,have considerably less extreme pressure properties.

The phosphonates which are used in preparing the compositions of theinvention are those having the general formula:

wherein R represents an alkyl group having from about 2 to 20,preferably 3 to 6, carbon atoms. These phosphonates are prepared fromthe corresponding phosphites by a Michalis-Arbusov rearrangement with analkyl halide catalyst. The products used in the working examples of theinvention were commercially available grades obtained from theVirginia-Carolina Chemical Co. of Richmond, Virginia. Examples ofcompounds coming under the above formula include dibutoxy butylphosphonate; monopentoxy, dibutoxy lauryl phosphonate, diethyl-hexylhexane phosphonate, didecyl decane phosphonate, etc.

While phosphonates of the above formula were found very eifective andstable, other rather related phosphorusoxygen compounds have variousdisadvantages. Thus phosphites, such as dibutyl phosphite, were found tohave extremely poor temperature stability, while phosphates were alsobad in this respect. The phosphites and phosphates attack rubber andclutch plates.

The base oil used is preferably a mineral lubricating oil having aviscosity of about to '500 SUS at 100 and a viscosity index of about to120. Preferred mineral oils are those having viscosities of 100 to 200SUS at 100 F. and viscosity indexes of to 105. These mineral oils may bederived from either parafiinic or naphthenic crude oils which arerefined by conventional methods. If the ester-phosphonate mixture is tobe used for a heavy industrial gear oil application, however, heavyoils, asphalts, waxes, etc. may be used to thicken the product.

The esters and phosphonates of the invention are also useful insynthetic oil compositions uch as polysilicone oils, diester oils suchas di-Z-ethylhexyl sebacate, glycol ether oils such as the Ucon oils,formals, polyearbonates, etc.

The final oil compositions will generally contain .5 to 10.0 wt. percentof the mercapto acid ester and about .5 to 10.0 wt. percent of thephosphonate depending on the molecular weight of the components and theend use of the oil. Preferred compositions will contain about 1.0 to 5.0wt. percent of the ester and 0.5 to 3.0 wt. percent of the phosphonate.Concentrates of the ester and phosphonate in oil may also be prepared.

The above compositions may also contain various other additives such asthickeners, viscosity index improvers, .pour point depressants,antioxidants, rust inhibitors, other extreme pressure additives,antiwear additives, etc.

Preferably, a viscosity index improver is utilized in amounts of .5 to10.0 wt. percent, preferably 1.0 to 5.0 wt. percent of activeingredient, based on the total weight of the finished composition. Theviscosity index impr-overs can be used to thicken low viscosity baseoils to the prefer-red viscosity for a transaxle lubricant (e.g. 150 to300 SUS at 100 F.). These viscosity index improvers are long-chainedpolymers of about 10,000 to 1,000,000 molecular weight. Examples of suchmaterial include polyisobutylene; copolymers of vinyl acetate anddialkyl fumar-ates or maleates; polymethacrylates, etc.

The invention will be further understood by the following examples whichinclude a preferred form of the invention.

EXAMPLE I PREPARATION OF ESTER FROM TALLOW ALCOHOL AND MERCAPTO ACETICACID (THIOVANIC ACID) An ester of the invention was prepared on a pilotplant scale. A commercial alcohol derived from the reduction of tallowfatty acids was used, which is manufactured by Archer Daniels MidlandCorporation and known as Adol 63. It consists roughly of straight chainC alcohol and /3 C alcohol and is a solid with a melting point of 55 C.In the preparation of the ester, gallons of hexane was charged to a gal.Dowtherm jacketed glass-lined reaction kettle. A 50 lb. bag of tallowalcohol was added in chunks, and low heat turned on the jacket. Afterminutes the alcohol had dissolved in the hexane solvent, and thetemperature rose to 107 F. in the kettle. The stirrer was turned on,17.8 pounds of thiovanic acid was added and the vacuum adjusted toprevent fumes. I-Ieat was increased slowly for one hour until the hexanestarted a very gentle reflux (145 F. kettle temperature). This refluxwas held for 24 hours while the water of reaction (1621 g.) was trappedoff. Then the return was cut off and the hexane drawn off for 30minutes. Vacuum and heat were gradually applied and the remainder of thehexane removed over one and one-half hours, reaching 220 F. and 29.3" Hgvacuum. The product was cooled to about 150 F. and drawn through a paperfilter into pails for storage. The yield was 64.17 pounds of crudeester.

A base stock was prepared having the following ingredients by weight:

46.9 parts low cold test Coastal distillate of 76 SUS/ 100 F. and 63V.I.

46.9 parts Mid-Continent neutral, 150 SUS/ 100 F. and

5.0 parts Additive A 1.0 part Acryloid 710 0.2 part Additive B Theinspections on this base stock blend are:

Gravity, API 30.8 S.U.S. vis./100 F. 181.3 S.U.S. vis./2l0 F. 48.6 Pour,F 35 Cloud, F 6 Flash, COC, F 360 :Fire, coo, F s85 Additive A is a 33wt. percent solution of polyisobutylene of about 10,000 molecular weightin 67 wt. percent of a solvent neutral mineral oil of 150 S.U.S.viscosity at 100 F.

The Acryloid 710 was a polymethacrylate viscosity index improver.

Additive B consisted of 37 /2 volume percent of a copolymer of Lorol Bfumarate and vinyl acetate, 12.5 volume percent of the condensationproduct of chlorinated wax and naphthalene and 50 volume percent of aneutral mineral oil of S.U.S. at 100 F. The copolymer is primarily aviscosity index improver while the condensation product is a pourdepressant.

To 100 parts by weight of the above base stock was aded 2 parts byweight of the tallow alcohol ester of mercapto acetic acid preparedabove, and 1 part by weight of dibutoxy butyl phosphonate (obtained fromVirginia Carolina Chemical Co.).

The resulting final composition was subjected to a series of testsdescribed as follows:

OLDSMOBILE 26A DOUBLE SHOCK TEST Here the oil composition was tested asa rear axle oil. First nineteen miles of warm-up driving was madebetween 40 and m.p.h. without any hard accelerations. Next, the auto wasaccelerated [at wide open throttle from to 100 m.p.h., then with closedthrottle the auto was allowed to coast from 100 back to 60 m.p.h. Thiswas repeated 10 times. The following shock cycles were then run:

(a) From a stop, a set brakes, fully open throttle with transmission indrive, release brakes and accelerate to 50 mph Pull shift lever into L0range and allow car to coast to a stop with the throttle closed.

b) From a stop, set brakes, fully open throttle with transmission indrive, release brakes and accelerate to 60 m.p.h. Pull shift lever intoL0 range and allow car to coast to a stop with the throttle closed.

(c) From a stop, set brakes, fully open throttle with transmission indrive, release brakes and accelerate to m.p.h. Pull shift lever into L0range and allow car to coast to a stop with the throttle closed.

Following these shock cycles, ten more wide open throttle 60 to 100m.p.h. accelerations with subsequent coastings were made.

The entire preceding test was then repeated, i.e. ten 60 to 100 m.p.h.accelerations, 3 shock cycles, ten 60 to 100 m.p.h. accelerations.

Upon completion of the 26A test the carrier was removed from the axleand disassembled for inspection. The composition passed the test. driveand coast sides of the tooth surfaces of the pinion and ring gear werenegligible.

The very light trace scoring observed on the gears caused this test tobe rated 2, a pass on the General Motors GMR rating scale.

CORVAIR SHOCK TEST This rear axle test was run on a 1960 Corvair with astandard transmission. The auto was driven as follows:

Step 1: 5 miles 50 m.p.h. Step 2: 5 miles 60 m.p.h. Step 3: 25 milesm.p.h. Step 4: Decelerate to 40 m.p.h.

The effects on the Step (a) Accelerate to 65 m.p.h. in third gear (b)Turnotf ignition (c) Disengage clutch (d) Coast to 60 m.p.h. 5 (e) Dropin clutch rapidly (f) Overrun to 40 m.p.h. (g) Turn on ignition Repeatsteps (a) through (g) times gtep 5: Shift to second gear and decelerateto m.p.h.

tep 7:

(a) Accelerate to 45 m.p.h. in second gear (b) Turn off ignition (c)Disengage clutch (d) Coast to 40 m.p.h. 15 (e) Drop in clutch rapidly(f) Overrun to 20 m.p.h. (g) Turn on ignition Repeat steps (a) through(g) 10 times.

After the above test, the gears were examined, and showed no scoring,and were rated Pass.

L-89 POWERGLIDE TEST This test is the standard CRC L-39 test which wascarried out on a Powerglide transmission over a period of 300 hours. Theoil temperature in the sump was 275 F. while the oil outlet temperaturefrom the converter was 300 F. No air was injected intothe transmisiso-n.

The results obtained are summarized in Table I as follows:

Table I TRANSMISSION TESTS Clutch plate condition Excellent. Nylon gearTrace wear. Valve body Clean. Screen Trace deposits. Sludge and varnishNone.

Rating Pass, excellent.

CHEVROLET POWERGLIDE 5000 MILE= ACCELERATION TEST This test was carriedout by operating a 348 cubic in. displacement engine connected to a2-speed Chevrolet Powerglide transmission. This mechanism wasautomatically operated on a dynamometer stand by means of a tapecontrolled electronic system. From an engine speed equivalent to about10 miles per hour, the engine was operated under maximum throttle untilit shifted from L0 to drive gear and had reached its maximum speed r indrive gear, at which point the engine was decelerated to a speed ofabout 10 miles per hour. A brake signal was interposed every secondcycle. This test was repeated for 5,000 miles at the rate of one fullcycle every one and a half minutes for a period of time of about 10 daysor 7,000 cycles. At the end of this time the transmission wasdisassembled and examined for wearor As indicated by the preceding data,the composition of Example I was excellent as a transmission lubricant,comparing favorably with the best of conventional detergent-inhibitortransmission oils.

10,000 MILE ACCELERATION TEST The test oil was used in the rear axle ofthe Chevrolet test car while 10,000 miles of acceleration testing wascompleted as described above. All parts of the axle were functioning andin excellent condition. Only a normal 6 burnishpattern was observed onthe ring and pinion gear after the test period. This indicates that theoil of invention satisfactorily lubricates a rear axle under severeprolonged actual car operation.

EXAMPLE II A transaxle base oil composition was prepared by mixing 91.4wt. percent of mineral lubricating oil, 6.78 wt. percent of Additive A,1.6 wt. percent of Acryloid 710, 0.22 wt. percent Additive B and .0012wt. percent of Dow Corning Silicone Fluid 200 as an antifoamant. To 96.8wt. percent of this base oil composition was added 2.0 wt. percent ofthe ester of tallow alcohol and mercapto acetic acid, 1.0 wt. percent ofdibutyl butane phosphonate, 0.1 wt. percent of Nonisol 210 as a rustinhibitor and 0.1 wt. percent of mercapto acetic acid as a supplementalextreme pressure agent. This lubricant composition was charged to thedifferential and transmission of a Corvair, wherein the differential andtransmission had been piped together so that the lubricant approachestest conditions anticipated in a transaxle employing a common lubricant.5500 miles of road test was satisfactorily completed with thiscomposition.

EXAMPLE III 96.9 wt. percent of base stock (same as in Example I)containing 3.0 wt. percent of the tallow mercaptoacetate plus 0.1 wt.percent Nonisol 210 was subjected to testing in a 1960 Chevrolet in theChevrolet Powerglide 5,000 mile acceleration test previously described.This oil contained no phosphorus additive. After 3,100 miles, the rearaxle developed :a loud whine and the temperature rose sharply. Ondisassembly, the ring and pinion gears showed severe iidging distress.In comparison, Example I, the rear end oil containing both themercapto-ester and the phosphonate had been allowed to run 10,000 mileswithout change, and at the end of this time all dif ferential parts werein excellent condition. This indicates that the combination of the esterand the phosphonate are required for adequate lubrication of the rearaxle differential under these extreme conditions of re peatedaccelerations. The transmission parts of Example III when compared withthose of Example I, showed several more small pits on the clutch platesand severe wear on the converter bronze thrust washer. While, theperformance of the transmission in Example III was satisfactory,however, the combination of both the sulfur and phosphorus additives asin Example I gave superior performance over that obtained using thesulfur additive alone.

EXAMPLE IV A number of esterifications were carried out using the sameequipment and procedure of Example I. Example I was repeated, exceptthat 0.37 pounds of NaI-ISO -H O Was added as a catalyst. This resultedin the water coming off in about three hours.

The mercapto esters of other alcohols were made. In the case of alcoholsbelow C chain length, it was necessary to wash the ester with N-aHCO inorder for the product (when dissolved in oil) to perform satisfactorilyin the 13-665 rust test with distilled water. It is also interesting tonote that the esters of lower molecular weight alcohols required longerreaction times than tallow alcohol. The secondary alcohols also requirelong reaction times, but this is to be expected.

The esters prepared above were added to a base oil composition which wasthe same as that described in Example II, These compositions were testedfor loadcarrying ability in a standard SAE laboratory test using a 3.4rubbing ratio at 1,000 r.p.m., and were also tested for wear in a4-bal-1 machine operating under 1-0 kilograms load, for ten minutes at1,800 r.p.m. and C. It is very important that the ester does notdeteriorate the buna rubber seals used in automatic transmission. Thus,the buna rubber seals themselves are relatively inexpensive, but it isnecessary substantially to dismantle the entire unit in order to replacethe seals. Rubber screening tests were carried out as follows: Sectionsof buna rubber compound (Acadia Rubber Co.) similar to the rubber us dfor transmission seals were out to lengths of /2" to 2". These stripshad a Shore A hardness of 71. The resulting strips were immersed in theoil composition in a 30 cc. beaker, covered, and stored in an oven at300 F. for 100 hours. The strip was removed from the hot test oil,placed in a beaker of original cool test oil for /2 hour, washed inacetone, wiped and immediately subjected to a Shore durometer A hardnessdetermination, The higher the number, the harder the rubber. The sidesof the beaker mentioned above were also examined for deposits to checkthe stability of the composition at high temperatures.

A multiple oxidation test was also run as follows: the oil compositionwas stored for 5 days at 300 F. in a beaker while stirring with a steelwire stirrer, and in the presence of a copper strip. At the end of thistime, drops of the oil composition was filtered through a #1 Whatmanpaper filter which was then examined for deposits. Also the copper stripwas examined, as well as the wire stirrer for the existence of varnishdeposits.

The compositions tested and results obtained are summarized in thefollowing table:

phosphonate in specific base oil compositions, said ester andphosphonate are equally applicable to other base oil compositions. Thus,the good efi'ects obtained by said ester and said phosphonate wereindependent of the other additives present, e.g. the V1. improvers andpour depressant, these other additives being present merely to give therequired low pour point and viscosity-temperature relationship necessarytor commercial transaxle lubricants. In sum, the present inventionrelates to lubricants which can be used for transaxle lubrication andwhich have any suitable base oil composition to which is added themercapto acid ester and phosphonate of the invention.

What is claimed is:

1. A lubricating oil composition suitable for lubrication of tr-ansaxlesystems, comprising a major amount of mineral lubricating oil, about 0.5to 10.0 wt. percent of a mercapto acid ester of the general formulawherein n is an integer of 1 to 4 and R represents a C to C alkylradical, and about 0.5 to 10.0 wt. percent of a phosphonate of thegeneral formula:

ROP=O wherein R is a C to C alkyl group.

Table IV Buna Rubber, Mult. Oxid. Test 5 Da./300 F. Wt SAE 4 Da./300 F.Alcohol Time, NaI-ISOl Perpercent Test 4 Ball Hrs. Catalyst cent S Esterin (Scale Test Oil Base lbs.) Shire Deposits Paper Cu Varn.

44 22. 5 0. 96 360 266 83 'Ir-l- Tr 42 22. 1 0. 96 410 .333 85 Tr+ O 321.8 0. 96 340 .419 82 Lt. 0 Cyclohexy] 72 17. 7 1.04 375 319 85 Tr+ 0Cyclohexyl 4 l. 04 305 81 Tr 0 41 15. 8 1. 24 315 289 84 Tr+ Tr 15. 0 1.24 400 452 86 Tr+ 0 42 14. 8 1. 24 305 469 81 0 0 30 12.5 1.60 310 28982 Tr+ Gray Ta 0 24 12. 1 1. 74 325 255 79 Hvy. Blaek Blk. O 30 7. 9 2.240 241 80 0 Gray Tan Blk 0 24 9. 8 2.0 310 82 1 The 011 base consistedof by weight, 46.2% Neeton 37, 45.2% Solvent 100 Neutral, 6.78% AdditiveA, 1.60% Acryloid 710, 0.22%

Additive B and .0012% DC-200 polysilicone antifoamant.

EXAMPLE V Using the base oil composition of Example IV, compositionswere made up containing the tallow thiovanate of Example I, and thebutyl phosphonate of Example I, as well as a mixture of the two. Thesecompositions were then tested for rubber hardening following theprocedure used in Example IV. Following are the results obtained.

Table V Shore A Treatment:

Untreated rubber Base oil composition 85 98 wt. percent base oilc0mp0sition-I-2 wt. percent ta'llow thiovanate 83 99 wt. percent baseoil composition+1 wt. per

cent butyl phosphonate 72 97 wt. percent base oil composition-P2 wt.percent tallo-w t-hiovanate-ll wt. percent butyl phosphonate v 73 Thesedata indicate that the oil of invention, will have no deter-iorativeeffect on rubber seals.

Similar laboratory screening tests with sections of clutch plate (G.M.part No. 3,748,703) and with nylon washers 1%" diameter indicate thatthe oil of invention should not be deleterious to transmission partsmade of these materials.

While the preceding examples have illustrated the invention by using thecombined mercapto acid ester and HS (CH CO OR wherein n is an integer of1 to 4 and R represents a C to C alkyl radical, and about 0.5 to 3.0 wt.percent of a phosphonate of the general formula:

wherein R is a C to C alkyl group.

5. -A lulbricatingoil composition suitable for lubrication of transaxlesystems comprising a major amount of 9 mineral lubricating oil, about1.0 to 5.0 wt. percent of a mereapto acid ester of the general formula:

HS(H COOR wherein n is an integer of 1 to 4 and R represents a CReferences Cited by the Examiner UNITED STATES PATENTS Sullivan25'2-49.8 =Rosen 252-336 X Burke et a1.

-Rosen '260481 X Moreton 252-499 DANI'EJL E. WYMAN, Primary Examiner.

JULIUS GREENWALD, Examiner.

1. A LUBRICATING OIL COMPOSITION SUITABLE FOR LUBRICATION OF TRANSAXLESYSTEMS, COMPRISING A MAJOR AMOUNT OF MINERAL LUBRICATING OIL, ABOUT 0.5TO 10.0 WT. PERCENT OF A MERCAPTO ACID ESTR OF THE GENERAL FORMULA: